Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Spectroscopic properties of Pr3+ doped in tellurite glass
Introduction
The luminescent properties of rare earth ions depend on the matrix in which these ions are placed. Glasses are an inherently disordered medium and the environment of the rare earth ions in glass is not uniform as in a crystal. This leads to a site-to-site variation in the energy levels and in the radiative and non-radiative transition probabilities for the rare earth ion. Glasses are being used as host materials for the solid state lasers and in many cases are more suitable than a crystal as a host. It has been observed that the fluorescence intensity of the rare earth ion is enhanced several fold when a glass host having low phonon energy i.e. one with heavy metal oxide, fluoride, germanate, tellurite, etc. is used [1], [2]. At higher concentrations of the rare earth a variety of new effects have been observed [3]. These include “pseudodiffusion”, line shape and line width variations for the non-resonant transitions, and variations in the 1/e lifetime for the excited state as a function of the absorption frequency. The depopulation of the excited states 3P0 and 1D2 of Pr3+ ions in LiPrxLa1−xP4O12 crystal has been analyzed from luminescence measurement [4]. High resolution polarized absorption and fluorescence spectra of Pr3+ in LiYF4 have been measured by Esterowitz et al. [5] at temperatures between 10 and 300 K. The lifetime of the excited state is determined by competing radiative and non-radiative decay processes, the latter (non-radiative) includes decay by ion-ion interactions (concentration quenching) and the emission of phonons.
Hegarty et al. [6] studied the 3P0 fluorescence decay in a LaF3 host doped with 20% PrF3, and by fitting their data to the Inokutti–Hirayama model [7] have determined the cross-relaxation interaction as an electric dipole–dipole one. In contrast to it Vial et al. [8] have identified the macroscopic cross-relaxation to be a short-range super-exchange interaction, if the concentration of Pr3+ in LaF3 is low. Mahato et al. [9] have also studied the spectrum of this ion in oxyfluoroborate glass. The luminescence property of Pr3+ ion doped in several other oxides, fluorides, fluorozirconate and sulphate glasses have been studied by several other workers [10], [11], [12], [13], [14].
Triply ionized Pr is known to lase in the orange and red regions of the spectrum when pumped with two Ti-Sapphire lasers at 1010 and 835 nm [15]. Judd–Ofelt theory [16], [17] has normally been used to analyze the absorption spectra of rare earth ions in different solid hosts but has been found to be unsatisfactory for some of the Pr-doped glasses [18], [19], [20] when hypersensitive transitions are included. In this paper we have studied the spectroscopic properties of Pr3+ doped in tellurite glass. Judd–Ofelt theory [16], [17] has been used (excluding the absorption transition 3F2 ← 3H4) to analyze and explain the experimental observations. The radiative lifetime of the 3P0 and 3P1 states of Pr3+ are compared with their values in other lattices. The concentration dependent fluorescence studies have been made and the mechanism of quenching discussed. The effect of temperature on the fluorescence intensity and the lifetime of the levels have also been studied.
Section snippets
Experimental
The following composition of TeO2, Li2CO3 and Pr2O3 (with 99% purity) have been used to prepare the glass.(80 − x) TeO2 + 20Li2CO3 + xPr2O3where x varies from 0.25 to 1.0 mol% of Pr2O3.
All these chemicals were made into fine powder in a ceramic mortar and finally mixed properly. The homogeneously mixed sample was then heated up to 730 °C in a platinum crucible for 1 h. The melt was constantly stirred for homogeneous mixing and then suddenly poured into a steel cast kept at 350 °C, and then pressed with a
Absorption spectrum
The absorption spectrum of the triply ionized Pr3+ doped tellurite glass shows different absorption peaks. It is seen that the absorption transitions of Pr3+ doped in tellurite glass are nearly the same as observed in other lattices though they differ in intensity. The observed bands arise due to transition from the ground state 3H4 to various excited states and their relative intensities vary from one host to another. The oscillator strength (Fexp) for the different bands were obtained from
Acknowledgements
Authors are grateful to C.S.I.R. and DST New Delhi for financial assistance.
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2021, Journal of LuminescenceCitation Excerpt :Considering the lighting field, Pr3+-doped systems have been gaining potentiality as orange/red-emitting activators, excited in the UV or blue light, extremely interesting for applications as a solid-state light source [11], sensors [12], lasers [13] and light-emitting diodes (LEDs) [14]. The blue emission (3P0→3H4) in Pr3+-doped materials has been observed only for Pr3+ ions into low phonon energy host, mostly fluorides and tellurites [15–19]; since the multiphonon relaxation from the 3P0 to the 1D2 frequently takes place, due to its dependence on the phonon energy of the system and the energy gap between the excited electronic states of the RE3+ [20]. Nevertheless, emission in the blue range is equally or even more important considering its application as scintillators [21], white light-emitting diodes (WLEDs) [22], and also lasers [17].